1. Field of the Invention
The present invention is directed to a method for purifying a crude oil in preparation for shipping, transporting or refining.
2. Description of the Related Art
Sulfur-containing crude oils continue to be a challenge for the shipper and refiner. Sulfur compounds in crude may present hazards to those engaged in handling, transporting or shipping the crude. They may introduce corrosion issues for transportation vessels, storage vessels, reaction vessels, separation vessels, piping and pumps used in the transportation and handling of sulfur containing crudes. They may introduce unique challenges for distilling such sulfur-containing crude oils.
U.S. Pat. No. 6,841,062 describes a crude oil desulfurization process which comprises hydrodesulfurizing a crude oil feed in a crude desulfurization unit. As described, when the product sulfur is maintained at less than 1 wt % based on feed, and preferably less than 0.75 wt % based on feed, reaction conditions in the crude desulfurization unit include a reaction temperature between about 315° C. and 440° C. (600° F.-825° F.), pressures from 6.9 MPa to about 20.7 MPa (1000-3000 psi), and a feed rate (vol oil/vol cat hr) from 0.1 to about 20 hr−1. Hydrogen circulation rate is general in the range from about 303 std liter H2/kg oil to 758 std liters H2/kg oil (2000-5000 standard cubic feet per barrel).
Some crude oils contain significant amount of unstable sulfur compounds. Under mild heating, these sulfur components react by hydrolysis and/or thermal degradation to form volatile sulfur compounds, including H2S. These reactions usually result in a slow but continuous hydrogen sulfide generation during the transportation of those crudes, which is one of the major risks or hazards on transporting such crude oils. These reactions also cause difficulties in refining those crude oils. At high temperature, as in the atmospheric and the vacuum distillation towers, the H2S production rate in the overhead of a distillation tower may be high enough to cause upsets in the tower. Currently, there is no existing technology to remove or convert unstable sulfur compounds in the crude oils, and crude containing high unstable sulfur has to be blended with other crudes in refineries. Overall, the need for blending severely limits the refiner's capacity in processing these unstable sulfur containing crudes. As a result, such crudes are usually sold at a discount in the market. Thus, solving the H2S evolution problem could substantially improve both the marketability and the value of crudes such as Eocene.